Rubber composition with silica reinforcement obtained with an amino acid or amino acid-containing protein based activator and use thereof in tires

ABSTRACT

The invention relates to the preparation of a silica reinforced rubber composition where alkoxysilane and/or sulfur cure reactions within the elastomer host are controlled by the use of a selected amino acid, or amino acid-containing protein based, activator. The invention also relates to such composite and to a tire having at least one component of such composite.

The Applicants hereby incorporate by reference prior U.S. ProvisionalApplication Serial No. 60/344,883, filed on Dec. 21, 2001.

FIELD OF THE INVENTION

The invention relates to the preparation of a silica reinforced rubbercomposition where alkoxysilane and/or sulfur cure reactions within theelastomer host are controlled by the use of a selected amino acid, oramino acid-containing protein based, activator. The invention alsorelates to such composite and to a tire having at least one component ofsuch composite.

Such amino acid-containing proteins are defined as proteins whichcontain one or more of such selected amino acids to enhance theformation of the alkoxysilane condensation reaction product within anelastomer host, to enhance the silane/elastomer interactions as well asto provide some unique synergism with the sulfur cure system for theelastomer composition Such amino acid-containing proteins are referredto herein as “derived protein(s)” as being the condensation product ofamino acids of which at least one of such amino acids is a selectedamino acid as defined and required by this invention.

The invention also relates to such composite and to a tire having atleast one component comprised of such composite

BACKGROUND OF THE INVENTION

Elastomer compositions typically contain particulate fillerreinforcement such as, for example, carbon black and/or silica.

Silica reinforcement for an elastomer composition may be provided byadding particulate silica such as, for example, precipitated silica, toa rubber composition.

In practice, particularly where a particulate silica-based filler isadded to an elastomer composition as an elastomer reinforcement such as,for example, an aluminosilicate or silica-modified carbon black, acoupling agent is often used to aid in coupling the filler to one ormore diene-based elastomers. The use of various coupling agents for suchpurpose is well known to those having skill in such art.

Such coupling agents may be, for example, an alkoxyorganosilanepolysulfide which has a constituent component, or moiety, (thealkoxysilane portion) capable of reacting with, for example, silanolgroups, on the silica surface of the silica-containing filler and, also,a constituent component, or moiety, (the polysulfide portion) usuallycapable of interacting with the rubber, particularly a diene-based,sulfur vulcanizable rubber which contains carbon-to-carbon double bonds,or unsaturation. In this manner, then, the coupler may act as aconnecting bridge between the silica-containing filler and the rubberand, thereby, enhance its reinforcing effect for the rubber composition.

In particular, it is envisioned that the silane moiety of the coupler,particularly a trialkoxysilane moiety, is available for reacting withvirtually any reactive hydroxyl groups it may encounter and particularlywith silanol groups (—Si—OH) on the surface of the silica-based fillerand also with alkoxy groups on the coupler itself to form siloxane units(—Si—O—Si—).

In practice, alkoxyorganosilane polysulfides sometimes used arebis-(3-trialkoxysilylalkyl)polysulfides which contain from about 2 to 8,with an average of from about 3.5 to 4.5, sulfur atoms in itspolysulfidic bridge.

During a typical mixing (processing) of the elastomer composition in aninternal rubber mixer under high shear conditions to temperatures in arange of 150° C. to 175° C., the silane portion reacts with the surfaceof a silica-based filler (e.g.: which may be hydroxyl groups on thesurface of the silica which may be in a form of silanol groups).

A portion of the polysulfidic bridge of such organosilane polysulfidetypically breaks during such mixing operation, resulting in an exposedsulfur on the coupling agent which is available to apparently interactwith one or more of the elastomer(s) in the elastomer composition.

However, it is to be appreciated that such interaction of the sulfurwith the elastomer(s) is typically accompanied by an increase in theviscosity (e g. Mooney viscosity) of the rubber composition itself asthe sulfur interacts with the elastomer(s). Too high of an elastomerviscosity under such conditions makes the rubber composition moredifficult to process, or mix, in a typical internal rubber mixer.

Therefore, a degree of adjustment of various formulation ingredients(formulation tuning) and enhancement of various physical properties islimited because of such typical higher viscosity related processinglimitations imposed via use of such coupling agent.

Uniquely, however, organosilane polysulfide compounds in a form oforganosilane disulfide compounds with predominately contained only abouttwo sulfur atoms in the polysulfidic bridge (e.g. and an average ofabout 2 to about 2.6 sulfur atoms) do not ordinarily cause suchexcessive viscosity build-up of the rubber composition during itsinternal mixing operation.

Such phenomenon in the use of the organosilane disulfide compounds isapparently due to stronger sulfur-to-sulfur bonds for the polysulfidicbridge of the disulfide and their inherent resistance to breaking uponhigh shear mixing at the aforesaid elevated temperatures, thus, enablingonly a very limited amount of sulfur atoms available to interact withdiene-based elastomer(s) in the rubber composition during the mixingoperation. This phenomenon is well known to those having skill in suchart.

Accordingly, it is desired to more effectively utilize the aforesaidrubber processing advantages afforded via use of such organosilanedisulfide compound, including a bis-(trialkoxyorganosilane)disulfide,compound as a coupling agent.

It is a purpose of this invention to enhance the formation of thealkoxysilane condensation reaction product within an elastomer host, toenhance the silane/elastomer interactions as well as to provide someunique synergism with the sulfur cure system for the elastomercomposition

While it is known from said EP Publication No. 1 061 097 that silicareinforcement may be improved by a condensation reaction of analkoxysilane, particularly an alkoxysilane polysulfide promoted orretarded by the presence of acidic or base materials, the use of aspecific type of amino acid, or proteins containing such amino acid, asdescribed herein and required for this invention is believed to be noveland inventive.

The term “phr” as used herein, and according to conventional practice,refers to “parts of a respective material per 100 parts by weight ofrubber, or elastomer”.

In the description of this invention, the terms “rubber” and “elastomer”if used herein, may be used interchangeably, unless otherwiseprescribed. The terms such as “rubber composition”, “compounded rubber”and “rubber compound”, if used herein, are used interchangeably to referto “rubber which has been blended or mixed with various ingredients andmaterials” and “rubber compounding” or “compounding” may be used torefer to “the mixing of such materials”. Such terms are well known tothose having skill in the rubber mixing or rubber compounding art.

The term “derived protein(s)” as used herein is intended to mean aminoacid-containing protein(s) which contains one or more amino acidsspecified herein available to interact with organosilanes and/or sulfurcure systems as discussed herein unless otherwise indicated.

SUMMARY AND PRACTICE OF THE INVENTION

In accordance with this invention, a process of preparing a composite ofan elastomer composition which contains a silica-based reinforcementtherein comprises the sequential steps of:

(A) thermomechanically mixing in at least one preparatory mixing step toa temperature of about 140° C. to about 190° C., alternatively to atemperature of about 150° C. to about 185° C.,

(1) 100 parts by weight of at least one sulfur vulcanizable elastomerselected from homopolymers and copolymers of conjugated dienehydrocarbons copolymers of at least one conjugated diene hydrocarbon andvinyl aromatic compound,

(2) about 15 to about 100, alternatively about 30 to about 90, phr ofparticulate filler comprised of at least one silica-based filler whichcontains reactive hydroxyl groups on the surface thereof (e.g.: silanolgroups),

(3) about 0.05 to about 20 parts by weight per part by weight of saidparticulate filler of at least one organosilane compound, preferably apolysulfide compound and, more preferably, a disulfide selected from atleast one of Formula (I) and (II), preferably Formula (I), theirmixtures:

Z—R¹—S_(n)—R¹—Z  (I)

Z—R¹—X  (II)

wherein n has a value of from 2 to 8 with an average of from 3.5 to 4.5,or an integer of from 2 to 4 with an average of from 2 to 2.6;

wherein Z is selected from the group consisting of:

wherein Z is preferably (Z3);

wherein R¹ is selected from the group consisting of a substituted orunsubstituted alkylene group having a total of 1 to 18 carbon atoms anda substituted or unsubstituted arylene group having a total of 6 to 12carbon atoms, preferably alklylenes having from 2 to 6 carbon atoms;wherein R² may be the same or different and is individually selectedfrom the group consisting of alkyls having 1 to 4 carbons and phenyl;and R³ may be the same or different and is individually selected fromR⁴O— radicals wherein R⁴ is an alkyl group containing from 1 to 4 carbonatoms, preferably from methyl and ethyl groups and more preferably anethyl group; and

wherein X is selected from mercapto, thiocyanato, amino, vinyl, epoxide,acrylate and methacrylate groups, preferably mercapto, epoxide and aminegroups;

(B) mixing therewith, preferably subsequently mixing therewith, at leastone amino acid as an alkoxysilane condensation reaction promoter, silaneelastomer interaction promoter and/or as sulfur cure system activatorfor the elastomer composition and/or derived protein which contains atleast one of said amino acids, wherein said amino acid(s) is of thegeneral Formula (III):

R—C(NH₂)(COOH)  (III)

wherein R is selected from one of Formulas (IV), (V), (VI) and (VII):

R⁵C═O(NH₂)  (IV)

R⁵SH  (V)

R⁵S—SR  (VI)

 R⁵OH  (VII)

wherein R⁵ is an alkyl radical containing from 1 to 6, alternativelyfrom 1 to 3 carbon atoms or an aryl radical (or alkyl substituted arylradicals) which contain from 6 to 12, alternately from 6 to 10 carbonatoms, and

wherein R⁶ is an alkyl radical containing from 1 to 6, alternativelyfrom 3 to 6 carbon atoms or an aryl radical (or alkyl substituted arylradicals) which contain from 6 to 12, alternately from 6 to 10 carbonatoms;

(C) subsequently blending sulfur therewith, in a final thermomechanicalmixing step at a temperature to about 100° C. to about 130° C.

For said final mixing step, usually elemental sulfur is added in anamount of about 0.4 to about 3 phr.

For said specified amino acids for use in this invention, representativeexamples of R⁵ and R⁶ are, for example, —CH₂ for R⁵ and—CH₂—C(NH₂)(COOH) for R⁶.

Representative examples of specified amino acids of Formula (III) areglutamine and asparagine as (NH₂)C═OCH₂CH₂C(NH₂)(COOH) and(NH₂)C═OCH₂C(NH₂)(COOH), respectively, where R is of Formula (VI),cysteine as HSCH₂C(NH₂)(COOH) where R is of Formula (V); cystine as(COOH)(NH₂)CCH₂SSCH₂C(NH₂)(COOH) when R is of Formula (VI), serine andthreonine as HOCH₂(NH₂)(COOH) and HOCC(CH₃)C(NH₂)(COOH), respectively,when R is of Formula (VII).

Preferably, said specified amino acid is cysteine, namely where R isR⁵SH from (Formula (V).

Said specified amino acids are designated for use in this invention on abasis that they are understood to not only participate as activators foractivation of the silane condensation reaction, but also have an abilityto react with a diene based elastomer or an ability to actsynergistically with the cure activators for sulfur cure systems forcuring the diene-based elastomer compositions.

For example, the cysteine and cystine amino acids are considered hereinas being useful as promoters for the silane condensation reaction withinthe elastomer host, as being interactive with diene-based elastomers(e.g. cis 1,4-polybutadiene, cis 1,4-polyisoprene and styrene/butadieneelastomers), perhaps with carbon-to-carbon bonds therein although themechanism is not entirely understood, to enhance various physicalproperties of the resultant elastomer and also useful as beingsynergistic with sulfur cure accelerators to accelerate the cure ofrubber compositions with accelerators such as for example,mercaptobenzothiazole based accelerators curatives and sulfenamide basedaccelerators.

For example, glutamine and serine amino acids are considered herein asbeing useful as promoters for the silane condensation reaction,particularly an alkoxysilane condensation reaction, within the elastomerhost and also useful as being synergistic with sulfur cure acceleratorsto accelerate the cure of rubber compositions with accelerators such asfor example, mercaptobenzothiazole based accelerators curatives andsulfenamide based accelerators.

It is considered herein that such specified amino acids or the derivedproteins as activators for the silane condensation reaction aresignificantly differentiated from protein based activators such as wheyprotein isolate, vegetable protein isolate and peptides containing oneamino group selected from arginine, lysine, hydroxylsine, histidine,proline, hydroxyproline, tryptophane and leucine.

In practice, the silica-based fillers are preferably selected from atleast one of aggregates of precipitated silica, aluminosilicate andsilica-treated carbon black having silica domains on its surface,wherein said precipitated silica and silica domains of said silicatreated carbon black contain hydroxyl group (e.g. silanol groups) ontheir surface.

In one aspect of the invention such process is provided wherein saidpreparatory mixing is conducted in at least two sequentialthermomechanical mixing steps in at least one internal rubber mixer;wherein at least two of said mixing steps are conducted are conducted toa temperature in a range of about 140° C. to about 190° C., withintermediate cooling of the rubber composition between at least two ofsaid mixing steps to a temperature below about 50° C.

In practice, the total, cumulative period of mixing, namely period ofmixing in an internal rubber mixer(s), for the said preparatory mixingstep(s) (A) may, for example, be in a range of about 3 to about 20,alternatively about 5 to about 15, minutes.

In practice, the period of mixing for the final thermomechanical mixingstep, namely period of mixing in an internal rubber mixer, (B) may, forexample, be in a range of from about one to about five minutes.

In further accordance with process of this invention, said preparatorymixing step (A) is composed of at least two sequential mixing stages inwhich said elastomer, said particulate silica-based filler and saidorganosilane polysulfide compound, preferably an organosilane disulfidecompound, are added and mixed in one or more sequential mixing stagesand in which said specified amino acid or derived proteins based silanecondensation reaction promoter or inhibitor is added subsequently to theaddition of both of said particulate filler and organosilane polysulfidein the same or subsequent mixing stage.

In additional accordance with the process of this invention, saidpreparatory step (A) is composed of at least two sequential mixingstages in which about 20 to about 60 weight percent of each of the saidsilica-based filler, and said organosilane polysulfide compound,preferably an organosilane disulfide compound, are added and mixed in afirst preparatory mixing stage and the remainder thereof added and mixedin at least one subsequent preparatory mix stage and the specified aminoacid or derived proteins based silane condensation promoter or inhibitoradded and mixed subsequent to the completed addition of said filler andorganosilane polysulfide in the same or subsequent mixing stage.

In practice, the organosilane polysulfide compound, preferably saidorganosilane disulfide compound, is optionally added to thethermomechanical preparatory mixing step in a form of a particulatecomprised of

(A) about 25 to about 75, preferably about 40 to about 60, weightpercent of said organosilane polysulfide compound and, correspondingly,

(B) about 75 to about 25, preferably about 60 to about 40, weightpercent carbon black.

A purpose of providing the organosilane polysulfide compound in a formof a particulate in the process of this invention is to add theorganosilane disulfide in a form of a relatively dry, or substantiallydry, powder in which the carbon black acts as a carrier for theorganosilane polysulfide in the process of this invention, particularlywhere the organosilane polysulfide would normally otherwise be in aliquid, or substantially liquid, form A contemplated benefit for theparticulate is to aid in the dispersing of the organosilane polysulfidein the preparatory mixing step(s) of the process of this invention andto aid in the introduction of the organosilane polysulfide into thepreparatory mixing of the rubber composition mixture.

In further accordance with this invention, a rubber composition isprovided which is prepared by the process of this invention.

In additional accordance with the invention, the process comprises asubsequent step of sulfur vulcanizing the prepared rubber composition,preferably at a temperature in a range of about 140° C. to about 190° C.

Accordingly, the invention also thereby contemplates a sulfur-vulcanizedrubber composition, prepared by the process of the invention.

In additional accordance with the invention, the process comprises theadditional, subsequent steps of preparing an assembly of asulfur-vulcanizable rubber composition having at least one component ofan unvulcanized (or vulcanized) rubber composition prepared by theprocess of this invention and vulcanizing the assembly at a temperaturein a range of about 140° C. to about 190° C.

In one aspect of the invention, such assembly is a tire and, preferably,such component is a tire tread.

Accordingly, the invention also comprises a vulcanized tire prepared bysuch process.

Also, accordingly, the invention comprises said tire wherein the saidcomponent is a tread.

In a further aspect of the invention, optionally a total of about 0.05to about 5 phr of at least one alkoxy silane, preferably an alkyl alkoxysilane, can be thermomechanically mixed in said preparatory mixingstage(s), particularly where said alkoxy silane has the formula:R³—Si—(OR⁴)₃, where R⁴ is a methyl, ethyl, propyl or isopropyl radical,preferably a methyl and/or an ethyl radical and R³ is a saturated alkylradical having from 1 to 18, alternatively from 2 to 6, carbon atoms, oran aryl or saturated alkyl substituted aryl radical having from 6 to 12carbon atoms. Such aryl or substituted aryl radicals might be, forexample, benzyl, phenyl, tolyl, methyl tolyl, and alpha-methyl tolylradicals.

A purpose of the alkoxy silane is, for example, to improve fillerincorporation and compound aging. Representative examples of alkylalkoxy silanes are, for example but not intended to be limited to,propyltriethoxysilane, methyltriethoxy silane, hexadecyltriethoxysilane,and octadecyltriethoxysilane

For an additional aspect of this invention, optionally from about 5 toabout 40 phr of a starch composite of starch and plasticizer may bethermomechanically mixed in said preparatory mixing stage(s).

Such starch composite preferably has a softening point in a range ofabout 110° C. to about 160° C. according to ASTM No. D1228.

Starch conventionally has a softening point in a range of about 180° C.to about 220° C. which is above normal rubber compound mixingtemperatures. Accordingly, a starch/plasticizer combination, or as acomposite thereof, is used with the plasticizer component having amelting point below 180° C. such as, for example, poly(ethylene vinylacetate), cellulose acetate and diesters of dibasic organic acids, solong as they have a softening point below 180° C. and preferably below160° C. It is contemplated that such starch composites contain hydroxylgroups on the surface thereof which are available for reaction withcoupling agents as described below. Representative examples of use ofstarch composites in rubber compositions may be found, for example, inU.S. Pat. No. 5,672,639.

A significant feature of this invention is the utilization of a silanecondensation reaction promoter and/or inhibitor to control the rate ofin-situ formation of the polysiloxane network which is accomplished bythe condensation of the silane coupling agent within the rubbercomposition.

Accordingly, the silane condensation reaction may be facilitated, forexample, by a promoter where it is desired to increase the condensationreaction rate or by a condensation reaction inhibitor where it isdesired to retard the condensation reaction rate.

While the mechanism may not be completely understood, it is hypothesizedthat a polysiloxane-based network (e.g.: a network of at least partiallyentangled polysiloxane polymer chains) is created by an in-situformation of a polysiloxane-based polymer chain, resulting from silanecondensation promoted by said specified amino acid or derived proteinsbased condensation reaction promoter, extending into and within alreadyformed polymer chains of the elastomer host This phenomenon can takeplace at the interface (filler/elastomer) which means at the vicinity ofthe filler surface and/or in the polymer matrix.

For example, it is hypothesized that utilization of abis-(trialkoxyorganosilane)polysulfide compound, preferably abis-(trialkoxyorganosilane)disulfide compound, in combination with saidamino acid or derived proteins based silane condensation reactionpromoter for enhancing a reaction of thebis-(trialkoxyorganosilane)polysulfide compound with silanol groups onthe silica-based filler and, also, alkoxy moieties of thetrialkoxyorganosilane polysulfide compound, react to form a polysiloxanewhich in turn, may lead to formation of a polysiloxane network at thesurface of the filler and/or within the elastomer.

For another significant aspect of the practice of the invention, it isconsidered herein that a significant departure from past practice, whenusing a bis-(alkoxyorganosilane)disulfide compound which contains anaverage of from 2 to 2.6 sulfur atoms in its polysulfidic bridge is

(A) promoting a creation of the polysiloxane polymer network via therequired promotion of the alkoxysilane condensation reaction with thesaid specified amino acid or derived proteins based promoter, whichwould be accompanied by an expected increase in viscosity of the overallelastomer composition with, correspondingly, a somewhat adverse impactupon its processability because of the increase in rubber compositeviscosity yet, however,

(B) in the absence of viscosity-increasing sulfur moieties beingliberated because the bis-(alkoxyorganosilane)polysulfide compound is aprimarily a disulfide compound since it contains an average of only 2 to2.6, instead of the aforesaid 3.5 to 4.5, connecting sulfur atoms in itspolysulfide bridge

Indeed, it is the very use of a bis(alkoxyorganosilane) compound withthe aforesaid connecting sulfur units of the polysulfide bridge beinglimited to an average of 2 to 2.6, instead of using abis-(alkoxyorganosilane)polysulfide with an average of 3.5 to 4.5 sulfuratoms in its polysulfidic bridge that enables an operational freedom inprocessing the unvulcanized rubber composition to be able to tolerate aincrease in viscosity of the rubber composition via promoting theaforesaid silane condensation reaction with the use of said specifiedamino acid or derived proteins based promoter.

As hereinbefore discussed, another important feature of this inventionis that the specified amino acids or the derived proteins for use inthis invention are considered herein to not only participate asactivators for activation of the silane condensation reaction but, alsohave an ability to react with a diene based elastomer (such as, forexample, the cysteine and cystine amino acids) and/or are consideredherein to tend to be synergistic with sulfur cure systems, based uponsulfur cure accelerators such as, for example mercaptobenzothiazolebased accelerators and sulfenamide based accelerators for diene-basedelastomers (such as, for example, the glutamine and serine amino acids).

As a result, it is considered herein that a new method has beendiscovered to modify, or tune, various physical properties of elastomersvia use of chemical control via use of selected amino acids as silanecondensation reaction promoters within an elastomer host in addition tothe thermomechanical mixing conditions.

Such new method is based upon the use of said specified amino acid orderived proteins based materials to promote a condensation of analkoxysilane and/or alkoxysilane polysulfide within an elastomer host,to react with a diene based elastomer (such as, for example, thecysteine and cystine amino acids) and/or to be synergistic with sulfurcure systems, based upon sulfur cure accelerators such as, for examplemercaptobenzothiazole based sulfur cure accelerators for diene-basedelastomers (such as, for example, the glutamine and serine amino acids)instead of using an acidic or basic condensation promoter or a proteinbased promoter other than said specified amino acid based promoter whichprime utility would be as promoters for silane condensation reactions.

The actual selection of an individual specified amino acid basedcondensation reaction promoter for use in this invention will dependsomewhat upon the sensitivity of the rubber matrix, or composition,itself and the balance of desired physical properties. Such selectioncan readily be made by one having skill in such art.

Thus, the condensation reaction and the impact on the sulfur network maybe controlled by said specified amino acid or derived proteins basedcondensation reaction promoter depending somewhat upon the magnitude ofthe effect desired and the silica-based filler used.

Where it is desired for the rubber composition, which contains both asiliceous filler such as silica, alumina and/or aluminosilicates, carbonblack and silica-modified carbon black reinforcing pigments, to beprimarily reinforced with silica-based filler(s) as the reinforcingfiller, it is often preferable that the weight ratio of suchsilica-based fillers to carbon black is at least 1/10 and preferably atleast 10/1.

In one aspect of the invention, it is preferred that the silica-basedfiller is precipitated silica.

In another aspect of the invention, the filler is comprised of about 15to about 95 weight percent precipitated silica, alumina, aluminosilicateand/or silica-modified carbon black, correspondingly, about 5 to about85 weight percent carbon black; wherein the said carbon black has a CTABvalue in a range of about 80 to about 150.

In a practice of this invention, said filler can be comprised of about60 to about 95 weight percent of said silica, alumina, aluminosilicateand/or silica-modified carbon black, and, correspondingly, about 40 toabout 5 weight percent carbon black.

The aluminosilicate can be prepared, for example, by co-precipitation ofa sodium silicate and an aluminate. The preparation of aluminosilicatesis well known to those having skill in such art.

The silica-modified carbon black may be prepared, for example, byreacting carbon black with a siloxane or by co-fuming carbon black andsilica an elevated temperature. Such methods of modifying carbon blackwith silica are known to those having skill in such art.

Representative examples of bis-(alkoxyorganosilane)disulfides (FormulaI) include, for example, 2,2′-bis(trimethoxysilylethyl)disulfide;3,3′-bis(trimethoxysilylpropyl)disulfide;3,3′-bis(triethoxysilylpropyl)disulfide;2,2′-bis(triethoxysilylethyl)disulfide;3,3′-bis(triethoxysilylpropyl)disulfide;2,2′-bis(tripropoxysilylethyl)disulfide, 2,2′-bi(tri-secbutoxysilylethyl)disulfide; 3,3′-bis(tri-t-butoxysilylethyl)disulfide;3,3′-bis(triethoxysilylethyl tolylene)disulfide;3,3′-bis(trimethoxysilylethyl tolylene)disulfide;3,3′-bis(triisopropoxysilylpropyl)disulfide;3,3′-bis(trioctoxysilylpropyl)disulfide,2,2′-bis(2′-ethylhexoxysilylethyl)disulfide; 2,2′-bis(dimethoxyethoxysilylethyl)disulfide;3,3′-bis(methoxyethoxypropoxysilylpropyl)disulfide; 3,3′-bis(methoxydimethylsilylpropyl)disulfide; 3,3′-bis(cyclohexoxydimethylsilylpropyl)disulfide; 4,4′-bis(trimethoxysilylbutyl)disulfide,3,3′-bis(trimethoxysilyl-3-methylpropyl)disulfide;3,3′-bis(tripropoxysilyl-3-methylpropyl)disulfide;3,3′-bis(dimethoxymethylsilyl-3-ethylpropyl)disulfide;3,3′-bis(trimethoxysilyl-2-methylpropyl)disulfide;3,3′-bis(dimethoxyphenylsilyl-2-methylpropyl)disulfide;3,3′-bis(trimethoxysilylcyclohexyl)disulfide;12,12′-bis(trimethoxysilyldodecyl)disulfide;12,12′-bis(triethoxysilyldodecyl)disulfide;18,18′-bis(trimethoxysilyloctadecyl)disulfide;18,18′-bis(methoxydimethylsilyloctadecyl)disulfide;2,2-′-bis(trimethoxysilyl-2-methylethyl)disulfide;2,2′-bis(triethoxysilyl-2-methylethyl)disulfide;2,2′-bis(tripropoxysilyl-2-methylethyl)disulfide; and2,2′-bis(trioctoxysilyl-2-methylethyl)disulfide.

Representative examples of compounds according to Formula (II) are, forexample, mercapto propyl triethoxysilane, gamma-amino propyltriethoxysilane, vinyl triethoxysilane, gamma-glycidoxypropyltriethoxysilane, gamma-methacryloxypropyltriethoxysilane.

In general, preferred compounds according to Formula (II) aremercaptopropyltriethoxysilane, gamma-glycidoxy propyltriethoxysilane,gamma-aminopropyltriethoxysilane.

In the practice of this invention, as hereinbefore pointed out, therubber composition is comprised of at least one diene-based elastomer,or rubber. Suitable conjugated dienes are isoprene and 1,3-butadiene andsuitable vinyl aromatic compounds are styrene and alpha-methylstyrene.Thus, it is considered that the elastomer is a sulfur-curable elastomer.Such diene-based elastomer, or rubber, may be selected, for example,from at least one of cis 1,4-polyisoprene rubber (natural and/orsynthetic), and preferably natural rubber), emulsion polymerizationprepared styrene/butadiene copolymer rubber, organic solutionpolymerization prepared styrene/butadiene rubber, 3,4-polyisoprenerubber, isoprene/butadiene rubber, styrene/isoprene/butadiene terpolymerrubbers, cis 1,4-polybutadiene, high vinyl polybutadiene rubber (35 to90 percent vinyl), styrene/isoprene copolymers, emulsion polymerizationprepared styrene/butadiene/acrylonitrile terpolymer rubber andbutadiene/acrylonitrile copolymer rubber.

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3-butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to 55 percent. In one aspect, the E-SBR mayalso contain acrylonitrile to form a terpolymer rubber, as E-SNBR, inamounts, for example, of about 2 to about 30 weight percent boundacrylonitrile in the terpolymer

The solution polymerization prepared SBR (S-SBR) typically has a boundstyrene content in a range of about 5 to about 55, preferably about 9 toabout 36, percent. The S-SBR can be conveniently prepared, for example,by organo lithium catalyzation in the presence of an organic hydrocarbonsolvent.

The 3,4-polyisoprene rubber (3,4-PI) is considered beneficial for apurpose of enhancing the tire's traction when it is used in a tire treadcomposition. When used, it is usually used in a minor amount of therubber component(s) of a rubber composition (e.g.: 5 to 15 phr).

The 3,4-polyisoprene elastomer and use thereof is more fully describedin U.S. Pat. No. 5,087,668 which is incorporated herein by reference.

The cis 1,4-polybutadiene rubber is considered to be beneficial for apurpose of enhancing the tire tread's wear, or treadwear.

Such polybutadiene elastomer can be prepared, for example, by organicsolution polymerization of 1,3-butadiene as is well known to thosehaving skill in such art.

The cis 1,4-polybutadiene elastomer may be conveniently characterized,for example, by having at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber arewell known to those having skill in the rubber art.

In the practice of this invention, it is further contemplated thatalkoxysilane-terminated and tin coupled solution polymerization preparedelastomers may also be used.

The alkoxysilane-terminated elastomers may be prepared, for example, byintroduction of a chloro-alkoxysilane, chloro-alkylalkoxysilane or3,3′-bis-(triethoxysilylpropyl)disulfide, into the polymerization systemduring the preparation of the elastomer, usually at or near the end ofthe polymerization. Such termination of such elastomers and thepreparation thereof are well known to those having skill in such art.

Tin coupled elastomers are prepared by introducing a tin coupling agentduring the polymerization reaction, usually at or near the end of thepolymerization. Tin coupling of elastomers is well known to those havingskill in such art.

Representative of tin coupled diene-based elastomers are, for examplestyrene/butadiene copolymers, isoprene/butadiene copolymers andstyrene/isoprene/butadiene terpolymers.

In one aspect, it is preferred that a major portion, preferably at leastabout 50 percent, and more generally in a range of about 60 to about 85percent of the Sn bonds in the tin coupled elastomer, are bonded todiene units of the styrene/diene copolymer, or diene/diene copolymer asthe case may be, which might be referred to herein as “Sn-dienyl bonds”(or Si-dienyl bonds), such as, for example, butadienyl bonds in the caseof butadiene being terminus with the tin.

Creation of tin-dienyl bonds can be accomplished in a number of wayssuch as, for example, sequential addition of butadiene to thecopolymerization system or use of modifiers to alter the styrene and/orbutadiene and/or isoprene reactivity ratios for the copolymerization. Itis believed that such techniques, whether used with a batch orcontinuous copolymerization system, is well known to those having skillin such art.

The tin coupling of the elastomer can be accomplished by relativelyconventional means and is believed to be well known to those skilled insuch art.

Various tin compounds can be used for such purpose and tin tetrachlorideis usually preferred. The tin coupled copolymer elastomer can also betin coupled with an organo tin compound such as, for example, alkyl tintrichloride, dialkyl tin dichloride and trialkyl tin monochloride,yielding variants of a tin coupled copolymer with the trialkyl tinmonochloride yielding simply a tin terminated copolymer

Examples of tin modified, or coupled, styrene/butadiene might be foundin, for example, U.S. Pat. No. 5,064,910.

The vulcanized rubber composition should contain a sufficient amount ofsilica, and carbon black if used, reinforcing filler(s) to contribute areasonably high modulus and high resistance to tear. The combined weightof the silica, alumina, aluminosilicates and/or silica-modified carbonblack, as well as carbon black, as hereinbefore referenced, may be aslow as about 30 parts per 100 parts rubber, but is more preferably fromabout 35 to about 90 parts by weight.

While it is considered herein that commonly-employed siliceous pigmentsused in rubber compounding applications might be used as the silica inthis invention, including pyrogenic and precipitated siliceous pigments(silica) alumina, aluminosilicates, precipitated silicas are preferred.

The siliceous pigments preferably employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate. Suchprecipitated silicas are well known to those having skill in such art.

Such precipitated silicas might be characterized, for example, by havinga BET surface area, as measured using nitrogen gas, preferably in therange of about 40 to about 600, and more usually in a range of about 50to about 300 square meters per gram. The BET method of measuring surfacearea is described in the Journal of the American Chemical Society,Volume 60, Page 304 (1930).

The silica may also be typically characterized by having adibutylphthalate (DBP) value in a range of about 100 to about 350, andmore usually about 150 to about 300 cm³/100 g (ASTM D2414).

Further, the silica, as well as the aforesaid alumina andaluminosilicate may be expected to have a CTAB surface area in a rangeof about 100 to about 220 m2/g (ASTM D3849). The CTAB surface area isthe external surface area as evaluated by cetyl trimethylammoniumbromide with a pH of 9. The method is described in ASTM D 3849 for setup and evaluation. The CTAB surface area is a well known means forcharacterization of silica.

Mercury surface area/porosity is the specific surface area determined byMercury porosimetry. For such technique, mercury is penetrated into thepores of the sample after a thermal treatment to remove volatiles. Setup conditions may be suitably described as using a 100 mg sample;removing volatiles during 2 hours at 105° C. and ambient atmosphericpressure; ambient to 2000 bars pressure measuring range Such evaluationmay be performed according to the method described in Winslow, Shapiroin ASTM bulletin, Page 39 (1959) or according to DIN 66133. For such anevaluation, a CARLO-ERBA Porosimeter 2000 might be used.

The average mercury porosity specific surface area for the silica shouldbe in a range of about 100 to 300 m²/g.

A suitable pore size distribution for the silica, alumina andaluminosilicate according to such mercury porosity evaluation, isconsidered herein to be.

(A) five percent or less of its pores have a diameter of less than about10 nm;

(B) 60 to 90 percent of its pores have a diameter of about 10 to about100 nm;

(C) 10 to 30 percent of its pores have a diameter of about 100 to about1000 nm; and

(D) 5 to 20 percent of its pores have a diameter of greater than about1000 nm.

The silica might be expected to have an average ultimate particle size,for example, in the range of 0.01 to 0.05 micron as determined by theelectron microscope, although the silica particles may be even smaller,or possibly larger, in size.

Various commercially available silicas may be considered for use in thisinvention such as, only for example herein, and without limitation,silicas commercially available from PPG Industries under the Hi-Siltrademark with designations Hi-Sil 210, 243, etc; silicas available fromRhodia with, for example, designations of Zeosil 1165MP and Zeosil165GR, silicas available from Degussa AG with, for example, designationsVN2, VN3, Ultrasil 7000 and Ultrasil 7005, and silicas commerciallyavailable from Huber having, for example, a designation of Hubersil 8745and Hubersil 8715.

Representative examples of alumina for the purposes of this inventionare natural and synthetic aluminum oxide (Al₂O₃). Such alumina can besuitably, synthetically prepared, for example, by controlledprecipitation of aluminum hydroxide. For example, neutral, acidic, andbasic Al₂O₃ can be obtained from the Aldrich Chemical Company. In thepractice of this invention, the neutral alumina is preferred, however,it is considered herein that the acidic, basic and neutral forms ofalumina could be used. The neutral, or substantially neutral form isindicated as being preferential in order to use a form with reducednumber of surface hydroxyl groups as compared to the acidic form and,also, to reduce the basic sites of the alumina which are AlO-ions,representing a strong base, in order to reduce potential interferenceswith the desired reactions of the alumina with the organosilanedisulfide coupler

Representative examples of aluminosilicates for the purposes of thisinvention are, for example but not intended to be limited to, Sepioliteas a natural aluminosilicate which might be obtained as PANSIL fromTolsa S.A., Toledo, Spain and SILTEG as a synthetic aluminosilicate fromDegussa GmbH. Such aluminosilicates can be used as natural materials orsynthetically prepared, for example, as hereinbefore exemplified.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly-used additive materials suchas, for example, curing aids, such as sulfur, activators, retarders andaccelerators, processing additives, such as oils, resins includingtackifying resins, silicas, and plasticizers, fillers, pigments, fattyacid, zinc oxide, waxes, antioxidants and antiozonants, peptizing agentsand reinforcing materials such as, for example, carbon black. As knownto those skilled in the art, depending on the intended use of the sulfurvulcanizable and sulfur-vulcanized material (rubbers), the additivesmentioned above are selected and commonly used in conventional amounts.

Typical amounts of reinforcing type carbon blacks(s), for thisinvention, if used, are hereinbefore set forth. It is to be appreciatedthat the silica coupler may be used in conjunction with a carbon black,namely, pre-mixed with a carbon black prior to addition to the rubbercomposition, and such carbon black is to be included in the aforesaidamount of carbon black for the rubber composition formulation. Typicalamounts of tackifier resins, if used, comprise about 0.5 to about 10phr, usually about 1 to about 5 phr. Typical amounts of processing aidscomprise about 1 to about 50 phr. Such processing aids can include, forexample, aromatic, napthenic, and/or paraffinic processing oils. Typicalamounts of antioxidants comprise about 1 to about 5 phr. Representativeantioxidants may be, for example, diphenyl-p-phenylenediamine and otherssuch as, for example, those disclosed in The Vanderbilt Rubber Handbook(1978), Pages 344 through 346. Typical amounts of antiozonants compriseabout 1 to 5 phr. Typical amounts of fatty acids, if used, which caninclude stearic acid comprise about 0.5 to about 3 phr. Typical amountsof zinc oxide comprise about 2 to about 5 phr. Typical amounts of waxescomprise about 1 to about 5 phr. Often microcrystalline waxes are used.Typical amounts of peptizers comprise about 0.1 to about 1 phr. Typicalpeptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

The vulcanization is conducted in the presence of a sulfur-vulcanizingagent. Examples of suitable sulfur-vulcanizing agents include, forexample, elemental sulfur (free sulfur) or sulfur donating vulcanizingagents, for example, an amine disulfide, polymeric polysulfide or sulfurolefin adducts which are conventionally added in the final, productive,rubber composition mixing step. Preferably, in most cases, the sulfurvulcanizing agent is elemental sulfur. As known to those skilled in theart, sulfur vulcanizing agents are used, or added in the productivemixing stage, in an amount ranging from about 0.4 to about 3 phr, oreven, in some circumstances, up to about 8 phr, with a range of fromabout 1.5 to about 2.5, sometimes from 2 to 2.5, being usuallypreferred.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. Conventionally and preferably, a primary accelerator(s) isused in total amounts ranging from about 0.5 to about 4, preferablyabout 0.8 to about 1.5, phr. In another embodiment, combinations of aprimary and a secondary accelerator might be used with the secondaryaccelerator being used in smaller amounts (of about 0.05 to about 3 phr)in order to activate and to improve the properties of the vulcanizate.Combinations of these accelerators might be expected to produce asynergistic effect on the final properties and are somewhat better thanthose produced by use of either accelerator alone. In addition, delayedaction accelerators may be used which are not affected by normalprocessing temperatures but produce a satisfactory cure at ordinaryvulcanization temperatures. Vulcanization retarders might also be used.Suitable types of accelerators that may be used in the present inventionare amines, disulfides, guanidines, thioureas, thiazoles, thiurams,sulfenamides, dithiocarbamates and xanthates. Preferably, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator is preferably a guanidine, dithiocarbamate orthiuram compound.

The rubber composition of this invention can be used for variouspurposes. For example, it can be used for various tire compounds. Suchtires can be built, shaped, molded and cured by various methods whichare known and will be readily apparent to those having skill in suchart.

The invention may be better understood by reference to the followingexamples in which the parts and percentages are by weight unlessotherwise indicated.

EXAMPLE I

Sulfur-vulcanizable rubber compositions which contain silicareinforcement are prepared utilizing a relatively high puritybis(3-triethoxysilylpropyl)disulfide compound alternately in combinationwith a selected amino acid, namely cysteine.

Such rubber compositions are identified herein as Samples A, B and C,with Sample A being considered herein as a Control sample without thecysteine addition.

For Samples B and C, a specified amino acid, namely cysteine, is alsoadded in the non-productive mixing stage after the silica-based fillerand coupling agent have been added.

Rubber compositions containing the ingredients shown in Table 1 wereprepared in a BR Banbury internal rubber mixer via the aforesaidsequential three separate stages of mixing, namely, two preparatory mixstages followed by a final mix stage to temperatures of about 170° C.,170° C. and 120° C., respectively. The mixing time for the firstpreparation (non-productive) mixing step is variable and the mixingtimes for the second and third preparatory steps are about two minuteseach.

After each mixing step the rubber mixture was batched off on a mill,mill mixed for a short period of time, and slabs of rubber removed fromthe mill and allowed to cool to a temperature of about 30° C. or lower.

TABLE 1 Sample A B C Non-productive Mix Stage Elastomer¹ 100 100 100Cysteine 0 1 2 Oil 10 10 10 Antidegradant² 1 1 1 Silica³ 50 50 50Coupling agent⁴ 4 4 4 Productive Mix Stage Zinc oxide 2.5 2.5 2.5Stearic acid 3 3 3 Sulfur 2 2 2 Sulfenamide based accelerator 1.6 1.61.6 Diphenylguanidine accelerator 2 2 2 ¹Isoprene/butadiene (50/50)copolymer elastomer having a Tg of about −44° C. obtained from TheGoodyear Tire & Rubber Company ²A phenylene diamine type ³Zeosil 1165 MPsilica from Rhone Poulenc ⁴A liquid coupling agent available fromDegussa AG as Si266, as a bis-(3-triethoxysilylpropyl) disulfide havingan average of about 2.2 connecting sulfur groups in its polysulfidicbridge

TABLE 2 Sample A B C Ring Tensile 100% modulus (MPa) 1.84 1.9 1.97 300%modulus (MPa) 11.49 12.3 13.41 Break strength (MPa) 15.1 16.17 14.23Energy, J 92.11 96.81 73.21 Elongation at break (%) 378 378 331 Hardness(Shore A)  23° C. 61.2 60.9 61 Zwick Rebound - Original  23° C. 41 42.142.6 100° C. 75.5 77.2 77.9 RPA, Cured Compound T10 2.84 2.46 1.93 T905.84 5.33 4.48 Delta torque 8.05 7.48 6.84 G′ at 1% strain 1771 16671536 G′ at 50% strain 771 787 775 G′ at 50%/G′ at 1% 0.435 0.472 0.505Tan delta at 15% strain 0.196 0.147 0.096

From Table 2 it can be seen that the addition of the specified aminoacid, namely the cysteine for Samples B and C resulted in variousphysical properties superior to such physical properties of ControlSample A. In particular, it is seen that hot rebound property increasedsubstantially and the tan delta property decreased which are indicationsof reduced hysteresis for the rubber product (predictive for betterrolling resistance or vehicle fuel economy for a tire with a tread ofsuch rubber composition). The 300 percent modulus is observed toincrease gradually as the amount of the amino acid is increased atnearly the same hardness which should improve tire handling performancefor a tire with a tread of such rubber composition.

The initial cure time for Samples B and C, as compared to Control SampleA is reduced as shown by the T10 cure times. The subsequent T90 curetime is also reduced which is an advantage for a reduced cure cycle timeat equal or better compound physical properties such as the indicated300 percent modulus and Shore A hardness values.

EXAMPLE II

Sulfur-vulcanizable rubber compositions which contain silicareinforcement are prepared utilizing a relatively high puritybis(3-triethoxysilylpropyl)disulfide compound and alternately additionof a cystine amino acid.

Such rubber compositions are identified herein as Samples D and E withSample E being considered herein as a Control sample.

For Samples B and C, a specified amino acid, namely cystine, is alsoadded in the non-productive mixing stage after the silica-based fillerand coupling agent have been added.

Rubber compositions containing the ingredients shown in Table 3 wereprepared in a BR Banbury internal rubber mixer via the aforesaidsequential three separate stages of mixing, namely, two preparatory mixstages followed by a final mix stage to temperatures of about 170° C.,170° C. and 120° C., respectively. The mixing time for the firstpreparation (non-productive) mixing step is variable and the mixingtimes for the second and third preparatory steps are about two minuteseach.

After each mixing step the rubber mixture was batched off on a mill,mill mixed for a short period of time, and slabs of rubber removed fromthe mill and allowed to cool to a temperature of about 30° C. or lower.

TABLE 3 Sample D E Non-productive Mix Stage Elastomer¹ 100 100 Cystine 02 Antidegradant² 1 1 Oil 10 10 Silica³ 50 50 Coupling agent⁴ 4 4Productive Mix Stage Zinc Oxide 2.5 2.5 Stearic acid 3 3 Sulfur 2 2Sulfenamide type accelerator 1.6 1.6 Diphenylguanidine accelerator 2 2¹Styrene butadiene copolymer elastomers having a Tg of about −15° C.obtained as Solflex 2552 from The Goodyear Tire & Rubber Company ²Aphenylene diamine type ³Zeosil 1165 MP silica from Rhone Poulenc ⁴Aliquid available from Degussa AG as Si266, abis-(3-triethoxysilylpropyl) disulfide coupling agent, having an averageof about 2.2 connecting sulfur atoms in its polysulfidic bridge.

TABLE 4 Sample D E Rheometer - ODR TC 50 6.73 4.08 TC 90 26.46 25.56Ring Tensile 100% modulus (MPa) 2.01 2.35 300% modulus (MPa) 16.07 17.49Break strength (MPa) 16.85 16.5 Energy, J 76.14 74.3 Elongation at break(%) 327 302 Hardness (Shore A) 23° C. 66.3 68.5 RPA: Cured Compound T103.13 1.92 T90 7.30 6.45 Delta S′ 6.08 5.92 G′ at 1% strain 1388 1432 G′at 50% strain 924 942 G′ at 50%/G′ at 1% 0.666 0.658 Tan delta at 15%strain 0.051 0.057 Insoluble polymer (NP) % 54 63

This example shows substantially the same trends as those described inExample I but it emphasizes the impact on the cure being faster and theeffect on the insoluble rubber which increases with the addition of theamino acid which is an indication for a more efficient silanecondensation reaction.

This Example shows then the dual effect of the selected amino acidactivator both from a silane condensation standpoint and from a curesynergism aspect.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:
 1. A process of preparing a composite of anelastomer composition which contains precipitated silica reinforcementtherein comprises the sequential steps of: (A) thermomechanically mixingin at least one preparatory mixing step to a temperature of about 140°C. to about 190° C., (1) 100 parts by weight of at least one sulfurvulcanizable elastomer selected from homopolymers and copolymers ofconjugated diene hydrocarbons copolymers of at least one conjugateddiene hydrocarbon and vinyl aromatic compound, (2) about 15 to about 100phr precipitated silica which contains silanol groups on the surfacethereof, (3) about 0.05 to about 20 parts by weight per part by weightof said precipitated silica of at least one organosilane compoundselected from at least one of an organosilane polysulfide compound ofFormula (I) and an organosilane compound of Formula (II) their mixtures:Z—R¹—S_(n)—R¹—Z  (I) Z—R¹—X  (II) wherein n has a value of from 2 to 8with is an average of from 3.5 to 4.5, or an integer of from 2 to 4 withan average of from 2 to 2.6; wherein Z is selected from the groupconsisting of:

wherein R¹ is an alkylene group having a total of 1 to 18 carbon atoms;wherein R² is the same or different and is individually selected fromthe group consisting of alkyls having 1 to 4 carbons and phenyl; and R³is the same or different and is individually selected from R⁴O-radicalswherein R⁴ is an alkyl radical containing from 1 to 4 carbon atoms; andwherein X is a mercapto group; (B) mixing therewith at least one aminoacid comprised of cystein; (C) subsequently blending sulfur therewith,in a final thermomechanical mixing step at a temperature to about 100°C. to about 130° C.; wherein said preparatory mixing step (A) iscomposed of at least two sequential mixing stages in which saidelastomer, said precipitated silica and said organosilane compound areadded and mixed in one or more sequential mixing stages and in whichsaid amino acid is added subsequent to the addition of both of saidprecipitated silica and organosilane compound in the same or subsequentmixing stage.
 2. The process of claim 1 wherein said preparatory mixingis conducted in at least two sequential thermomechanical mixing steps inat least one internal rubber mixer; wherein at least two of said mixingsteps are conducted to a temperature in a range of about 140° C. toabout 190° C., with intermediate cooling of the rubber compositionbetween at least two of the said mixing steps to a temperature belowabout 50° C.
 3. The process of claim 1 wherein said preparatory mixingstep (A) is composed of at least two sequential mixing stages in whichsaid elastomer and about 20 to about 60 weight percent of each of saidprecipitated silica and said organosilane polysulfide are added andmixed in a first preparatory mixing stage and the remainder thereofadded and mixed in at least one subsequent preparatory mixing stage;wherein said amino based silane condensation promoter is added and mixedsubsequent to the completed addition said silica-based filler andorganosilane polysulfide in the same or subsequent mixing stage.
 4. Theprocess of claim 1 wherein the polysulfidic bridge of said organosilanepolysulfide contains an average of from 2 to 2.6 sulfur atoms.
 5. Theprocess of claim 1 wherein a total of about 0.05 to about 5 phr of atleast one alkoxy silane is further added to said preparatorythermomechanical mixing step(s); wherein said alkoxy silane has theformula: R³—Si—(OR⁴)₃, where R³ is selected from at least one of methyl,ethyl, propyl and isopropyl radicals and R⁴ is a saturated alkyl havingfrom 6 to 18 carbon atoms or aryl or saturated alkyl substituted arylradical having from 6 to 12 carbon atoms.
 6. The process of claim 5wherein said alkoxy silane is selected from one or more ofpropyltriethoxy silane, methyltriethoxy silane, hexadecyltriethoxysilane and octadecyltriethoxy silane.
 7. The process of claim 1 whereinabout 5 to about 40 phr of a starch composite comprised of starch andplasticizer is added in said preparatory mixing stage(s) (A); whereinsaid starch composite has a softening point in a range of about 110° C.to about 160° C. according to ASTM No. D1228.
 8. The process of claim 7where said plasticizer contains hydroxyl groups on the surface thereonand comprises at least one of poly(ethylene vinyl acetate), celluloseacetate and diesters of dibasic organic acids having a softening pointbelow 160° C.
 9. The process of claim 1 where said sulfur-vulcanizableelastomer is selected from at least one of natural and synthetic cis1,4-polyisoprene rubber, emulsion polymerization preparedstyrene/butadiene copolymer rubber, organic solution polymerizationprepared styrene/butadiene copolymer rubber, 3,4-polyisoprene rubber,isoprene/butadiene rubber, styrene/isoprene/butadiene terpolymerrubbers, cis 1,4-polybutadiene rubber, medium vinyl polybutadiene rubber(35 to 50 percent vinyl), high vinyl polybutadiene (50 to 75 percentvinyl) and emulsion polymerization preparedstyrene/butadiene/acrylonitrile terpolymer rubber andbutadiene/acrylonitrile copolymer rubber.
 10. The process of claim 1wherein said elastomer is an organic solution polymerization derivedelastomer selected from at least one of alkoxy terminated elastomer andtin coupled elastomer.
 11. A rubber composition prepared by the processof claim
 1. 12. A vulcanized rubber composition prepared by the processof claim 1 wherein said process comprises a subsequent step of sulfurvulcanizing the resulting rubber composition.
 13. A tire having at leastone component as the rubber composition of claim
 12. 14. The tire ofclaim 13 wherein said component is a tread.
 15. The process of claim 1which comprises a subsequent step of preparing an assembly of a sulfurvulcanizable rubber composition having at least one component of therubber composition prepared according to claim 1 and sulfur vulcanizingsaid assembly at a temperature in a range of about 140° C. to about 190°C.
 16. The process of claim 15 wherein said assembly is a tire and saidcomponent is a tread.
 17. A tire having at least one component comprisedof a rubber composition prepared according to claim
 1. 18. The tire ofclaim 17 wherein said component is a tread.